The present invention concerns dynamically controlled electronic locking systems. It relates more particularly to a locking system of the type including means for entering data, an electromagnetic actuating device for actuating a bolt and an electronic circuit.
Such a locking system is, for example, disclosed in U.S. Pat. No. 5,488,660. The opening thereof is controlled by a combination, given by a central unit and modified each time that the locking system is opened. Since the locking system and the central unit are not directly connected to each other, they must be able to work in synchronism, so that the code transmitted by the central unit can be verified as being correct by the locking system.
These locking systems are particularly intended to allow a single access to a protected space, for example to the inside of a cash dispenser, to assure the maintenance and loading thereof. They assure, in particular, that persons entrusted with a maintenance operation on one occasion are prevented from using the code which was transmitted to them to subsequently open the locking system. Consequently, it is not possible to have access to the protected space without previously obtaining an access code from the central unit managing the system. Security of access is therefore considerably increased.
More precisely, the locking system disclosed in the aforementioned Patent includes a keyboard for entering the combinations into the locking system, a display for displaying the information relating to the entry of data, and an electronic circuit for receiving the combination and comparing it to an authorised combination. The electronic circuit includes:
a device actuated when an entry combination is entered, to generate a combination from previously stored data;
a comparator, for comparing the entry combination with the generated combination and, in the event of equality, for sending signals for the control of the bolt and storage of new data.
In this locking system, the combination is obtained from mathematical operations which involve, inter alia:
the last accepted combination,
a parameter peculiar to the locking system,
a master combination, and
a value which varies according to a predetermined rule, for example, the number of openings.
The entry combination is defined by a computer of the central unit managing the system, which includes the same calculating means and stores in its memory the same data as the locking system. The combinations are calculated, both in the locking system and in the central unit, on the basis of numbers stored in the memory and by applying preestablished mathematical formulae. The locking system includes, in addition, comparing means for comparing the combination entered with the generated combination, the bolt being released if the combinations are equal.
 Combination  means a number entered into the locking system to be compared to a number generated in the locking system, these two numbers having to be equal.
By developing a different approach, in which the memory stored data are processed by means of logic functions, it is possible to achieve locking systems allowing security of access to be further improved.
The invention therefore includes means for entering data, an electromagnetic actuation device for controlling a bolt and an electronic circuit. It is characterised in that the electronic circuit includes:
a first memory for storing a reference value,
a second memory for storing a current value,
a processing unit including a first register for applying a function to the reference value, a second register for processing the current value, a third register for processing an entry value, means for transferring the reference value and the current value from its memory into its respective register and conversely, and logic means for:
processing the reference value contained in the first register to define a new reference value replacing the former value in the first register,
combining the current value contained in the second register and the entry value contained in the third register, to define a new current value replacing the former one in the second register,
comparing the content of the first and second registers, and
solely in the event of a match, sending an instruction to the electromagnetic actuation device to control the bolt, replacing, in the first memory, the reference value contained therein by the new reference value contained in the first register and replacing, in the second memory, the current value contained therein by the new current value contained in the second register.
Such a locking system requires a new access code upon each proper manipulation, which reduces the risk of unauthorised access, as mentioned hereinbefore, in a remarkably effective manner.
 Code  means a number or a word entered into the locking system and processed by the electronic circuit to give a value which, compared to another value which is also defined by the circuit, allows or does not allow opening of the locking system.
In a particular embodiment, the processing unit includes shift registers, each including a plurality of cells, numbered 0 to n and in which the last data item to be entered occupies the cell of the lowest row.
More precisely, the processing unit includes, in addition, three exclusive OR gates, each provided with two inputs and one output and defining, with the shift registers, linear feed shift registers (LFSR).
More particularly, the processing unit includes:
a value processing linear feed shift register, including a first shift register and an exclusive OR gate, for processing the former reference value in order to obtain a new reference value, and
a combination linear feed shift register, including a second shift register, into which the current value is entered, and a third shift register, into which the entry value is entered, and two exclusive OR gates for combining the current value and the entry value and for defining the new current value.
The processing unit further includes a logic processing unit arranged to check whether the cells of the same row of at least a portion of the first and second shift registers, have an identical content.
It should be noted that the system forming the subject of the aforementioned Patent leads to combinations which are perfectly determined. In other words, by knowing the algorithm, which can be achieved easily by using a system of this type, and by analysing several successive combinations, it is possible to define the subsequent combinations. Certainly, access to the locking system is made more difficult when the code does not change, but it is still possible, with relatively modest means, to generate the subsequent opening combinations on the basis of data which is relatively easy to obtain and thus to obtain access in an unauthorised manner to the protected space.
One important object of the present invention is to overcome this drawback. The locking system is therefore also characterised in that the processing unit is arranged so that it only compares a portion of the elements of the current value and the reference value. More precisely, the logic processing unit only takes account of a portion of the cells of the first and second shift registers.
The present invention also concerns a control system including a central device arranged to generate different successive control codes and a dynamically controlled locking system.
This control system is characterised in that the central device includes:
a first memory for storing a reference value, equal to the reference value contained in the first memory of the locking system,
a second memory for storing a current value, equal to the current value contained in the second memory of the locking system,
a processing unit including:
a first register for processing the reference value,
a second register for processing the current value,
means for transferring the reference value and the current value from its memory into its respective register and conversely,
means for processing the reference value contained in the first register, to define a new reference value replacing the value previously contained in the first register,
means for combining the current value contained in the second register and the new reference value, to define an entry value contained in a third register and a new current value contained in the second register.
In order to use the simplest possible means for the creation of the access codes, the control system is characterised in that the central device and the locking system include shift registers each including cells numbered from 0 to n, and in which the last data item to be entered occupies the cell of the lowest row.
In a particularly advantageous embodiment of the invention, the control system is characterised in that the locking system processing unit further includes three exclusive OR gates each provided with two inputs and one output, defining with said registers:
a value processing linear feed shift register, including a first shift register into which the reference value is entered and an exclusive OR gate for processing the former reference value in order to obtain a new reference value, and
a combination linear feed shift register, including a second shift register into which the current value is entered, and a third shift register into which the entry value is entered and two exclusive OR gates, for combining the current value and the entry value and for defining the new current value,
and in that the processing unit of the device further includes three exclusive OR gates and a switch together defining:
a value processing linear feed shift register, including a first shift register into which the reference value is entered, and an exclusive OR gate for processing the former reference value in order to obtain a new reference value, and
a combination and mixing linear feed shift register, including a second shift register into which the current value is entered, a third shift register into which the entry value is entered, and a fourth shift register into which a value originating at least mediately from the first shift register is entered, and two exclusive OR gates, for processing the value contained in the fourth register and the former current value, in order to obtain the entry value and a new current value.
In order to assure the data processing, the locking system processing unit further includes a logic processing unit for checking whether the cells of the same row of at least a portion of the first and second register have an identical content.
As was explained hereinbefore, analysis of successive codes and knowledge of the algorithm generating them can allow the future codes to be defined. Once the locking system is arranged so that only a portion of the data contained in the code is read by the comparator, it is possible to enter random values, thereby making determination of future codes illusory. The control system is therefore characterised in that the logic processing unit of the locking system is arranged so that it only compares a portion of the elements of the current value and the reference value and in that the processing unit of the central device further includes a logic processing unit for processing the reference value contained in the first shift register and for entering the post-processing value into the fourth shift register, a fifth shift register and a sixth shift register cooperating with the logic processing unit to respectively mask a certain number of cells of the first register and to enter a random value into cells whose elements are not subject to comparison.